Method of obtaining americium

ABSTRACT

1. IN A PROCESS FOR THE SYNTHESIS OF ELEMENT 95, THE STEPS WHICH COMPRISE DISSOLVING A NEUTRON-IRRADIATED MASS OF URANIUM CONTAINING A TRANSURANIC FRACTION COMPRISING PREDOMINANTLY PLUTONIUM WHICH CONTAINS AT LEAST ABOUT 0.01% OF THE ISOTOPE 94**241 AND A DETECTABLE QUANTITY OF ELEMENT 95 IN AN AQUEOUS ACIDIC SOLUTION, OXIDIZING THE PLUTONIUM CONTAINED IN THE RESULTING SOLUTION TO A VALENT STATE GREATER THAN +4, REMOVING URANIUM FISSION PRODUCTS AND ELEMENT 95 THEREFROM BY MEANS OF A WATER-INSOLUBLE RARE EARTH SALT CARRIER, DISSOLVING THE CARRIER PRECIPITATE THUS OBTAINED, INTRODUCING FLOUSILICATE IONS INTO THE RESULTING SOLUTION, CONTACTING SAID SOLUTION WITH A WATER-INSOLUBLE RARE EARTH SALT CARRIER FOR SAID FISSION PRODUCTS AND SEPARATING THE RESULTING PRECIPITATE, ADDING SUFFICIENT HYDROFLUORIC ACID TO RENDER THE SUPERNATANT SOLUTION THUS OBTAINED FROM ABOUT 3 TO 6 M WITH RESPECT THERETO, THEREAFTER CONTACTING THE SOLUTION WITH A WATER-INSOLUBLE RARE EARTH SALT CARRIER FOR ELEMENT 95, AND SEPARATING THE CARRIER PRECIPITATE FROM THE SOLUTION.

United States Patent METHOD OF OBTAINING AMERICIUM Stanley G. Thompson,Richmond, Califi, assignor to the 1 United States of America asrepresented by the United States Atomic Energy Commission No Drawing.Filed Aug. 23, 1946, Ser. No. 692,729

v Int. Cl. C01g 51/00; G21g 1/00 I US. Cl. 176-16 11 Claims The presentinvention relates to a new transuranic element. More particularly it isconcerned with the transuranic element having atomic number 95, nowknown as americium having the symbol Am, isotopes thereof, compositionscontaining the same, and methods of producing and purifying said elementand compositions thereof.

The expression element 95 is used throughout this description todesignate the element having atomic number 95. Reference herein to thiselement is to be understood as denoting the element generically whetherin its free state or in a form of a compound, unless otherwise indicatedby the context.

As far as is presently known two isotopes of americium have beensynthesized in identifiable quantities, i.e., Am and Am The formerisotope is an alpha emitter having a half-life of 500 years, while thelatter is a short-lived (17-18 hours half-life) beta emitter which istransformed relatively rapidly into element 96 known as curium andhaving the symbol Cm, an isotope of an other new transuranic element andan alpha emitter having a half-life of about five months. The alphaparticles emitted from this isotope have a range in air of 4.75 cm. Asecond isotope cm is produced by the bombardment of 94 with alphaparticles. This isotope has a half-life of thirty days and is also analpha emitter. The alpha particles produced thereby have a range of 5.0cm.

in arr.

In accordance with the present invention, it has been found that theseisotopes of element 95 can be produced in a variety of ways such as, forexample, by bombarding plutonium produced in a neutronic reactor, whichconsists essentially of isotope 94 together with a relatively smallconcentration of isotope 94 with subatomic particles, e.g., deuterons orneutrons. In preparing element 95 by the bombardment of 95 by thebombardment of plutonium with deuterons, for-example, these subatomicparticles should generally have energies of the order of at least mev.and preferably energies of 14 to 16 mev. or higher. The synthesis ofelement 95 in this manner is thought to involve at least a portion andvery probably all of the nuclear reactions indicated below:

9 241 9524! 2-20 years In general, it has been found that element 95 ismost conveniently synthesized in a neutronic reactor operated at arelatively high power level (about 200,000 kw.) for an extended periodof time (approximately 100 days). A suitable neutronic reactor which maybe employed in the preparation of element 95 is described and claimed inco-pending application for U.'S. Letters Patent, Ser. No. 568,904 ofEnrico Fermi and Leo Szilard, filed Dec. 19, 1944, now Pat. No.2,708,656. In such reactors a fissionable isotope, such as U in naturaluranium, undergoes fission and releases fast neutrons in excess of theneutrons absorbed in the fission process. The fast neutrons are sloweddown to approximately thermal energies by impacts with a moderator suchas graphite or deuterium oxide, and the resulting slow neutrons(energies of 0- 0.3 electron volt) are then absorbed by U to producefurther fission and by U to produce U which decays through 93 to 94 Thisself-sustaining chain reaction releases tremendous amounts of energy,primarily in the form of kinetic energy of the fission fragments. Withsuch reactors the maximum reaction rate for steady state operation isdetermined by the maximum rate at which the heat of reaction can beremoved. The rate of production of plutonium in such reactors may thusbe equated, approximately, to the power output of the reactor, andamounts to about 0.9 gram of 94 per megawatt day when operating withsufficient bombardment and aging times to permit total decay of 93 to 94A portion of the 94 thus produced in the reactor under such conditionsabsorbs neutrons to form the isotope 94 In neutronic reactors operatedunder the general conditions of power level and time indicated above theabsorption cross-section of 94 for the formation of 94 is rather large,amounting for thermal neutrons to nearly one-half the cross-section forthe fission or 94 Thus plutonium produced in the above manner frequentlycontains as much as 2% of the isotope 94 The latter isotope is an alphaemitter and also undergoes spontaneous fission to a slight extent(half-life for the process is 10 years). If this isotope is maintainedin a neutronic reactor for a substantial period after its formation, itis transformed into the next heavier isotope which, in general,constitutes about .01 percent of the total plutonium produced underconditions of power level and time indicated above. As previouslypointed out, 94 is a beta emitter and decays into 95 In a naturaluranium pile, or neutronic reactor operating at such substantial powersand for substantial periods of time, the formation of element 95(isotopes 95 and 95 and 96 is presumed to be synthesized in accordancewith the following series of nuclear reactions:

240 zlo 1 240 1 1 1 n n n The mechanism of formation of 94 as indicatedby the nuclear reactions written above is such that its concen trationin pile uranium is proportional to the third power of the specificneutron exposure and the ratio of its concentration to that of 94 isproportional to the second power of the specific neutron exposure.Hence, the amount of 95 which is formed per day per unit of plutonium inthe free or combined state is proportional to the second power of thespecific neutron exposure of the uranium from which the plutonium wasformed. Inasmuch as the decay of 94 to 95 occurs during as well as afterthe neutron bombardment period, the percentage of the latter in thetransuranic fraction can be controlled by varying the time ofbombardment, the time of aging subsequent to bombardment of uranium, orboth.

fission From an inspection of the above proposed nuclear reactions, itwill be apparent that the formation of element 95 is dependent on theconcentration of 94 which is in turn dependent upon the amount of 94produced. Also, while the desired concentration of element 95 in thetransuranic fraction of the product may be obtained by sufficientbombardment alone, it will be evident that a finite aging time willensue before the separation of element 95 from the bombarded product canbe effected. In the present description, therefore, it can be assumedthat the bombarded product is always aged and that the concentration ofelement 95 in the transuranic fraction of the product is controlled bythe total bombardment time plus aging. The figures below are indicativeof the proportion of 95 to 94 in a neutron bombarded uranium pi eoperating at a neutron flux of neutrons/cm sec. and at varyingconcentrations of 94 Pu gm./ton of uranium: 95 mg./ton of uranium Itwill be apparent that element 95 can be synthesized at neutron fluxesconsiderably lower than 10 neutrons/ cm. /sec.; however, at suchintensities the formation of element 95 will be proportionately slower.In general, however, it will be found that neutron fluxes of at least 10neutrons/cm. /sec. or higher are preferable.

Element 95 may be obtained from plutonium which has been previouslyisolated from uranium irradiated in a neutronic reactor of the typementioned above, in accordance with, for example, the procedure setforth in co-pending application, Ser. No. 637,484, filed Dec. 27, 1945,by Glenn T. Seaborg et al., now Pat. No. 3,190,804. In accordance withthis procedure, neutron bombarded uranium is dissolved in an aqueoussolution of a suitable acid such as, for example, nitric acid and theresulting solution, which contains the plutonium in the tetravalentstate and the uranium in the hexavalent or non-carriable state, iscontacted with a substantially insoluble, solid, finely divided compoundwhich is a plutonium carrier. The carrier precipitate thus obtainedcontaining plutonium is next separated from solution by any convenientmeans such as, for example, centrifugation or filtration after which theproduct precipitate is again dissolved and the plutonium removed fromsolution by a carrier which is chemically distinct from the one firstused. This procedure can be repeated if necessary. Also, a third carrierdifferent in chemical composition from the first two mentioned may beutilized in a third precipitation. The advantage of these alternatecarriers lies in the fact that certain impurities present in the processsolution can be eliminated by employing a plutonium carrier that doesnot remove particular impurities with it. By proper selection andrepeated application of such carriers, it will be seen that theseparation of plutonium in the form of a relatively pure compound can bereadily effected.

Metallic plutonium can be obtained by means of high temperaturereduction of a suitable halide thereof such as, for example, plutoniumtrifluoride, with a reactive metal such as lithium, calcium, barium,etc., in accordance With the procedure which is more fully described inthe aforementioned co-pending application, Ser. No. 637,484, thedisclosure of which is incorporated herein by reference.

Element 95 present in the plutonium obtained in accordance with theprocedure generally outlined above may be isolated therefrom by firstallowing the plutonium to age for a desired period of time in metallicor solution for-m, for example, a salt solution such as a solution ofplutonous nitrate, after which the bulk of the plutonium is separatedfro-m element 95 by the addition of a soluble peroxide to the solutionthereby converting plutonium to its substantially insoluble peroxide andleaving element 95 in solution as a soluble peroxide. The last traces ofplutonium which amount to about 1-5% of the plutonium originally presentin solution can be removed by performing a series of precipitationcycles which involve first destroying the excess peroxide in solution byheating and then converting element and the remaining plutonium to theirhydroxides by the addition of a suitable base such as, for example,ammonium hydroxide, whereby the plutonous hydroxide carries fromsolution element 95 in the form of its insoluble hydroxide. Theresulting precipitate is then dissolved in concentrated nitric acid orother suitable acid to form a solution of substantially less volume thanthe original, after which plutonium and element 95 are converted totheir respective peroxides and the above cycle repeated until analysisof the hydroxide precipitate by a pulse analyzer or other suitable alphapulse responsive means indicates that the alpha radiation of theprecipitate emanates substantially completely from the element 95content thereof. Impurities which form insoluble hydroxides, such asiron and aluminum, if present in interfering concentrations, can beconveniently separated from element 95 by utilizing a carrier for theplutonium and element 95 which, under certain conditions, will carrythese two elements leaving iron and aluminum in solution. A suitablecarrier for this purpose has been found to be potassium plutonousfluoride, K PuF Separation of aluminum and iron from plutonium andelement 95 is accomplished by adding potassium ions, for example, in theform of potassium nitrate, to the afore-mentioned solution of decreasedvolume formed by dissolving the plutonous hydroxide product precipitatein nitric acid, after which sufficient hydrofluoric acid is introducedto make the resulting solution about 1 M with respect to bothhydrofluoric acid and potassium nitrate. Under these conditions the ironand aluminum fluorides are soluble, whereas the fluoride of element 95is insoluble and is carried from solution by the insoluble K PuF Thelatter then can be converted to the sulfate by fuming with sulfuricacid, the sulfate dissolved in water, and the plutonium and element 95again precipitated in the form of their hydroxides by addition ofammonium hydroxide thereto. After the removal in this manner of aluminumand iron or other impurities whose hydroxides are insoluble, furtherseparation of the plutonium from element 95 by utilization of thehydroxide-peroxide precipitation cycle described above can be effected.

Element 95 is also found to be present in the fission productprecipitates obtained in accordance with the procedure of co-pendingapplication, Ser. No. 637,484, referred to above, when theseprecipitates are obtained by bombardment of plutonium-containing uraniumin a neutronic reactor operating at substantial powers for substantialperiods of time such as those specified above. The element is present inthese precipitates since it resists oxidation conditions under whichplutonium is oxidized to a valence state greater than +4 and hence isremoved from solution along with fission products, which consist chieflyof rare earth elements, as a result of a carrying step. In separatingelement 95 from solutions containing fission products and that element,the radioactive zirconium and barium present are removed prior to theseparation of the rare earth elements. Thus, zirconium can be readilyseparated from such solutions by contacting the latter with a suitablecarrier such as, for example, ceric iodate, while the radioactive bariumis separated from element 95 by precipitating the latter in the form ofits hydroxide in the presence of a suitable carrier, for example, ceroushydroxide.

In instances where bombardment periods are extensive, it is apparentthat appreciable quantities of element 95 will be formed during suchperiods as a result of the beta decay of 94 Thus, any of the 95 isotopeso produced passes into the fission product fraction during theseparation of plutonium from said fission products by precipitation ofthe fission products from an aqueous solution containing plutonium inthe hexavalent state. Because of the similarity of the chemicalproperties of the rare earths and element 95, as well as element 96, themajor diificulties encountered in the decontamination of these elementsare in the separation of the radioactive rare earth elements therefrom.This object can be satisfactorily accomplished, however, byprecipitating the rare earths in the presence of fluosilicate ions.Under these conditions element 95 appears to be converted to a solublecomplex, and the rare earths are removed by repeated precipitation witha suitable rare earth carrier such as, for example, lanthanum or cerousfluorides. After removal of said rare earths in this manner, element 95is separated from solution by carrying with a suitable rare earthfluoride in the presence of hydrofluoric acid. In a preferred embodimentof the above procedure the initial solution containing element 95 andfission products is made about 3 M in nitric acid and 1 M in fluosilicicacid, after which a quantity of a suitable trivalent salt of a rareearth metal such as, for example, cerium is added and the resultingsolution is allowed to stand until precipitation of the insoluble cerousfluoride and cerous fluosilicate thus formed appears to be complete.Such an operation results in the removal of about 90% of the rare earthspresent together with a relatively small quantity of element 95, i.e.,about The quantity of element 95 in the supernatant solution can then beremoved by making the solution from about 3-6 M in hydrofluoric acid,after which additional trivalent cerium is introduced whereby element 95is carried down with the cerous fluoride thus formed. This cycle can berepeated as many times as is considered necessary or desira ble.

As examples of compounds suitable for use in carrying element 95 fromthe atbove mentioned types of solutions in addition to those alreadyenumerated, there may be mentioned compounds of low water solubility(less than 0.01 mol per liter) such as bismuth oxalate, bismuthphosphate, manganese dioxide, and the insoluble rare earth metalcompounds such as the oxalates, iodates and fluorides thereof, and thelike. Other insoluble carriers such as, for example, bismuth phosphate,also function satisfactorily, especially in solutions of low acidity. Inthis connection it may be mentioned that the carriers listed above arelikewise useful in removing fission products from solution when element95 is in a noncarriable form, such as, for example, in the form of afluosilicate complex. Additional carriers for this purpose are zirconiumphosphate and zirconium iodate.

Inasmuch as various members of the class of carriers mentioned abovepossess the peculiar property of removing certain impurities fromsolution together with element 95 while not removing other impurities,such a property may be utilized in separating the aforesaid element byemploying alternate carriers capable of removing different impurities.The alternate use of K PuF and Pu(OH) as carriers for element 95 is atypical example of the principle contemplated by the foregoingstatement.

The insoluble carrier employed may be introduced into the solution as apreformed finely divided solid, but it is' preferably precipitateddirectly in the solution from which element 95 is thereby carried. Themechanism of the carrying of element 95 from solution is not accuratelyunderstood. However, it is believed it is effected in some cases, atleast, by incorporation of element 95 ions into the carrier crystallattice (frequently known as isomorphic carrying), in some cases bysurface absorption of element 95 ions, and in other cases by combinationof both.

The term carrier as applied to element 95 herein and in the appendedclaims is to be understood as signifying a substantially insoluble,solid, finely divided compound capable of ionizing to yield at least oneinorganic cation and to yield at least one anion which constitutes anionic component of a compound which contains the ion to be carried, saidlatter compound being not substantially more soluble in the samesolution than said finely divided compound. The preferred carriers forelement 95, at least in its trivalent state, comprise compounds havingan anion which is capable of forming an insoluble compound with a rareearth metal, such as lanthanum or trivalent cerium, in the samesolution. The term insoluble is used herein to designate compounds whichhave solubilities in water of the order of 0.01 mol/liter or below.

In separating element 95 from highly' radioactive contaminants such asare most of the fission products of uranium and plutonium, it isdesirable to minimize the carrying of such radioactivity associatedtherewith. One method of reducing the amount of radioactivity carried bya carrier precipitate is to introduce into the solution a radioactivelyinert diluent or hold-back carrier which is an inactive isotope of theradioactive isotope to be held back in the supernatant solution duringprecipitation of the carrier. This method is particularly effective forreducing the carrying of the radioactive isotopes carried by absorptionor other surface saturation type of carrying. Thus, inactive isotopes ofthe various uranium or plutonium fission products which are notisomorphic with the carrier cation may be employed to improve thedecontamination of element 95 when carrying it from solutions derivedfrom either neutron irradiated uranium or plutonium.

The carrying procedure may be effected by any of the known techniquesfor effecting adequate contact of liquids with insoluble solids. In thecase of pre-formed carriers the finely divided solid may be agitatedwith the solution or the solution may be continuously passed throughfixed beds of the carrier. As previously pointed out, the preferredprocedure is to precipitate the carrier directly in the solutioncontaining element 95. This operation may be accomplished by adding theion components of the carrier in any order; however, it is generallypreferred to add the cation first and then the anion. Mixed carriers maybe precipitated if desired by precipitating two or more cations with thesame anion, two or more anions withthe same cation, or byco-precipitating carriers differing in both cation and anion.

When employing any of the above procedures it is desirable to provide anadequate contact time or digestion period to insure adequate carrying ofthe element 95 This is particularly desirable in the case of isomorphiccarrying or other internal carrying. The digestion may be effected atroom temperature, but it is usually preferred to employ an elevatedtemperature ranging from about 30 C. to a temperature substantiallybelow the boiling point of the solution. Temperatures of 40 to 60 C.will generally be satisfactory, with a contact time or precipitatedigestion time of 10 to minutes, and preferably 30 to 60 minutes. Thecarrier may then be separated from the supernatant solution by anysuitable means, such as decantation, filtration or centrifugation.

In addition to the above method for separating element from solutionsthereof containing commonly associated impurities, separation of thatelement from such solutions may also be effected by the utilization of asuitable substantially water immiscible solvent which exhibits a specialselective solvent action on element 95 or on the impurities with whichit is associated. Likewise, qualitative separation of elements 95 by theaforementioned extraction process from a certain group of impuritiesnormally associated therewith such as, for example, compounds of therare earth metal group, is also contemplated by the present invention.

In its chemical and physical properties element 95 in numerous respectsdiffers widely from plutonium and resembles rather closely the rareearths as pointed out above. For example, element 95 is highly resistantto either vigorous oxidation or reduction, and while certain evidencehas indicated that this element does possess states of valence otherthan +3, the latter oxidation state has been found to be by far the moststable. The absorption spectrum of trivalent element '95 in an aqueousnitric acid solution has been determined and, aside from a generalabsorption in the ultraviolet range, there are only two markedabsorption peaks between 320 and 1100 millimicrons; one in the visiblerange at 503::1 millimicrons. The peak at 503 millimicrons is sharp witha molar extinction coeflicient of at least 300. The molar extinctioncoeflicient of the peak at 815 millimicrons is about 50. Addition ofpotassium bromate to a nitric acid solution of element 95 results in thedisappearance of the sharp peak at 503 millimicrons in a period of about15 minutes after which a slow recline of the peak occurs. Thisphenomenon appears to be conclusive evidence for the oxidation oftrivalent element 95 to a higher oxidation state. Under such conditionselement 95 may be oxidized to the tetravalent state, the pentavalentstate or to an even higher valence. In this connection is should bepointed out that potassium bromate is the only oxidizing agent employedthus far which has been found to be capable of converting said elementto a higher state of oxidation. Even such a relatively strong oxidizingagent as argentic ion has been unsuccessful in attempts to oxidizeelement 95 to the tetravalent or higher state.

Element 95 is capable of forming various organic complexes withcompounds which contain an atom capable of supplying a pair of electronsto a coordinate bond and thus form a coordination type of compound.Thus, compounds Which are capable of forming at least one coordinatebond and at least one other linkage such as a polar or nonpolar bondwith a metal atom will form complexes with element 95. Compounds of thistype include acids or alcohols which contain atoms capable of supplyingelectrons to a coordinating metal such as N" C=C, O-, fiS, NH *NH, etc.For example, element 95 forms a complex with benzohydroxamic acid whichhas the following probable structure:

This compound is soluble in organic solvents such as chloroform.Consequently element 95 may be removed from aqueous solution byagitation of the solution with a complexing agent of this type for 24-48hours, and then extracting the solution with chloroform or equivalentsolvent. Other acids or compounds containing trivalent nitrogen orsimilar atoms such as glycine, cupferron, salicylaldehyde, pyruvic acid,acetoacetic acid, etc., may be used in similar manner.

Element 95 also may be removed from aqueous solutions by reaction with abase exchange acid or salt such as the zeolite, or Amberlite IR resinswhich are a resinous condensation product of a phenol sulphonic acid orsulphonate and an aldehyde such as formladehyde. For example aqueoussolutions containing element 95 and rare earth fission products may becontacted with Amberlite IR1 a resin formed by reacting tannin withsodium bisulphate and condensing the product with formaldehyde. In sucha case the element 95 is adsorbed to form a salt of 95 and the baseexchange acid. This product which also contains rare earth or othermetals when they are present in the aqueous solution may be selectivelyeluted using a solution of cirtric acid having a pH of about 2.5 andunder such a case the 95 together with elements 61 and 62 may be elutedfrom the remaining rare earth elements which have been adsorbed.

The fact that the peroxide of element 95 is much more soluble thanplutonium peroxide makes possible a satisfactory method for separatingthese elements, although the hydroxide of element 95 is substantiallyinsoluble and is readily carried from solutions by plutonous hydroxide.

Volatilization tests indicate that at 1100 C. element 8 is approximatelytimes more volatile than plutonium.

Numerous compounds of element 95 have been pre pared and certain oftheir properties noted. Typical of those compounds which have beensynthesized are the hydroxide, the dioxide, the iodate, the trifluoride,and the trichloride. The procedures employed in the synthesis of thesecompounds as well as their various physical prop erties are given below.

The hydroxide of element 95 is relatively insoluble and can be formed byneutralizing a nitric acid solution of element 95. The hydroxideprecipitates in the form of a gelatinous mass and is white to pale pinkin color. In solutions 4 M in ammonium hydroxide and hydroxide ofelement 95 is soluble to the extent of about 10 mg./l.

The anhydrous trichloride of element 95 is prepared by reacting thedioxide With carbon tetrachloride at about 750 C. Under such conditionsa light yellow sublimate is obtained whose X-ray difiraction pattern istypical of the trivalent rare earth chlorides. This compound melts atapproximately 730 C.

The dioxide of element 95 constitutes the only clear evidence that thiselement has a stable tetravalent state. This compound may be prepared byigniting either the hydroxide or the nitrate. In the dry state the oxideis black; however, in water it dissolves and reverts to the trivalentstate to form a solution that is pink to violet in color. The X-raydiffraction pattern of the compound indicates a dioxide having a cubicface centered lattice with a constant, a=5.37i.01 A.

The iodates and trifluoride of element 95 have also been prepared byadding the respective acid to a solution containing element 95 which isabout 0.25 N in nitric acid. The hydrogen iodate or hydrogen fluoride isgenerally added in an amount sufiicient to render the solutionapproximately 0.1 N with respect to the particular acid introduced. Theiodate and trifluoride appear as cream colored gelatinous precipitates.

In addition to the various compounds of element 95 specificallydescribed above other compounds of that element such as the organicsalts and organic complexes thereof as well as additional mineral acidsalts may be prepared. Such compounds include the acetates, propionate,oxalate, tartrate, and citrate of element 95.

Element 95 may be obtained as the free metal by reduction of the oxide,fluoride, chloride, carbide, etc., with a highly active metal such as,for example, barium, calcium, magnesium, aluminum, etc., by employingtemperatures at or in the vicinity of the melting point of element 95The element in uncombined form may also be obtained by the electrolysisof suitable aqueous solutions thereof or by the electrolysis of moltensalts of element 95 such as the chloride or fluoride in the presence orabsence of alkali or alkaline earth metal halides.

The present invention may be further illustrated by the followingspecific examples.

EXAMPLE I A sample of neutron bombarded plutonium weighing 21.6 mg. wasdissolved in 9 ml. of 1.5 M nitric acid. The beta contaminants in thissolution amounted to 309 millieuries. The plutonium was precipitatedfrom solution in the form of its hydroxide by addition of an excess ofsodium hydroxide, after which the precipitate thus obtained and whichcontained element 95 was separated by centrifugation and washed. Theprecipitate was next dissolved in concentrated nitric acid diluted to10- ml. and thereafter heated at 90-100 C. for eighteen hours. 1 mg.each of barium and strontium ions were next added as hold-back carriers,after which lanthanum fluoride was precipitated in the solution by theaddition of 0.2 mg. lanthanum ions and hydrofluoric acid which had beentreated with potassium bromate to remove any reducing agents that mighthave been present. The precipitate thus obtained was separated bycentrifugation, washed, and then heated with 1 ml. of 20% sodiumhydroxide to convert the lanthanum, plutonium, and element 95 to theircorresponding hydroxides. This mass was next dissolved in concentratednitric acid, 0.2 mg. of argentous ion and a large excess of ammoniumpersulfate were added, the resulting mixture diluted to 2 ml. giving asolution 2 M in nitric acid, after which the latter was allowed to standfor one hour. Element 95 was then carried from solution by a lanthanumfluoride carrier formed by the addition of hydrofluoric acid. Thelanthanum fluoride precipitate thus obtained was next metathesized with20% sodium hydroxide solution in the manner set forth above, after whichthe mixture of converted hydroxides was dissolved in concentrated nitricacid. This solution was diluted to 2 ml. (1 M in nitric acid), made 0.05M in potassium dichromate, and then heated to 90100 C. for sixteenhours, after which element 95 was again carried from solution withlanthanum fluoride by the addition of hydrofluoric acid thereto. Underthe foregoing conditions any plutonium which might have been present issubstantially completely removed. At this stage of the separationprocess the lanthanum fluoride precipitate thus obtained was analyzedfor its plutonium and element 95 content by measuring its alpharadiation with a proportional counter. A total of 195,000 counts perminute was recorded, 30,000 of which were attributable to element 95.The beta radiation was measured by means of a calibrated electroscopeand was found to be 134 millicuries'. The aforesaid lanthanum fluorideprecipitate was next metathesized with 20% sodium hydroxide aspreviously described and the metathesized product dissolved inconcentrated nitric acid, after which 0.2 mg. of argentous ion and anexcess of ammonium persulfate were added. This solution was then dilutedto 2 ml. (2 M in nitric acid), allowed to stand for one and one-halfhours whereby the plutonium present therein was oxidized to thehexavalent state. Hydrofluoric acid was next added, and the lanthanumfluoride precipitate thus obtained was separated by centrifugation,washed, and again metathesized as above. The resulting product wasdissolved in concentrated nitric acid, the solution diluted andprecipitation again effected by the addition of ammonium hydroxide. Thisprecipitate was next dissolved in concentrated nitric "acid to give asolution 3 M with respect thereto, after which sufficient phosphoricacid was added to make the solution 0.1 M therein. To this solutiontetravalent zirconium ions were added in a concentration of 0.1 mg. perml., and the resulting mixture allowed to digest for 15 minutes at 50 C.The zirconium phosphate precipitate thus formed removed a substantialportion of the plutonium fission products present leaving element 95 insolution together with a quantity of rare earth activities. Element 95and the aforesaid rare earths were then removed by adding ammoniumhydroxide thereto, causing the rare earths and element 95 to precipitateas hydroxides. This hydroxide precipitate was dissolved in concentratednitric acid to give a solution 3 M therein, made 1 M in fluosilicic acidand 0.1 M in hydrofluoric acid, after which lanthanum ions were added ina concentration of 7.5 mg. per ml. and the mixture allowed to stand forone hour. The lanthanum fluoride precipitate thus obtained carried withit substantially all of the rare earth activities present in solution.After precipitation appeared to be complete, the precipitate wasseparated as above and the element 95 present in the mother liquor wasprecipitated as the hydroxide by adding ammonium hydroxide. Thisprecipitate was then dissolved in concentrated nitric acid, theresulting solution adjusted to an acidity of 5 M and lanthanum ionsadded in a concentration of 7 mg. per ml. at a temperature of about 35C. Thereafter 2.5 M fluosilicic acid was added over a period of one hourto give a solution which was 3.5 M in nitric acid, 0.8 M in fluosilicicacid and having a concentration of lanthanum ions of 5 mg. per ml. Theprecipitate thus obtained consisted essentially of lanthanum fluorideand lanthanum fluosilicate while the supernatant solution on analysis ofan aliquot thereof indicated that a total of 20,000 counts per minute ofelement 95 was present. The beta radiation in solution had beendiminished to a total of 0.17 millicurie. After repeating theabove-mentioned fluosilicate precipitation two more times, a supernatantsolution was obtained which contained a total of 14,000 counts perminute of element 95, the beta contamination being present only to theextent of 0.001 millicurie. By carrying out the above procedure, anover-all recovery of 35% was achieved, based on the total concentrationof element 95 originally present. The over-all decontamination factorattained was of the order of 1 X 10 EXAMPLE II A sample of plutoniumcontaining 0.015% of the beta emitting isotope 94 after having been agedfor a period of five weeks, was dissolved in 1.5 M nitric acid, afterwhich the plutonium present therein was substantially completelyprecipitated in the form of its peroxide by the addition of an excess ofaqueous hydrogen peroxide (30% H 0 by weight). After the plutoniumperoxide was separated by centrifugation, the supernatant solution washeated to decompose the peroxide present. The plutonium remaining insolution (50 mg.0.25 mg./ml.) was removed in the form of its hydroxideby the addition of ammonium hydroxide thereto, thereby carrying 98% ofelement 95 with it. The precipitate thus obtained was next dissolved in3 ml. of concentrated nitric acid and the plutonium again removed fromsolution by peroxide precipitation as described above. To the resultingsupernatant solution (plus washings from the plutonium peroxideprecipitate) which contained a total of 0.5 mg. of plutonium was addedpotassium nitrate and then hydrofluoric acid, each in an amountsuflicient to render the resulting solution 1 M therein. The insoluble KPuF thus formed removed element 95 but left in solution impurities suchas iron, aluminum, etc., which form insoluble hydroxides. More than ofelement was carried in this step. The K PuF was next converted to thesulfate by fuming with sulfuric acid, after which it was dissolved inwater, the hydroxide precipitated with ammonium hydroxide, and then thisprecipitate separated and dissolved in nitric acid. Plutonium peroxidewas again precipitated, this time from a volume of 50 l. Upondecomposition of hydrogen peroxide in the mother liquor, a gelatinousprecipitate was observed to form. On addition of hydrofluoric acid tothe solution a light crystalline fluoride precipitate appeared, whilethe gelatinous precipitate dissolved. This fluoride precipitate was nextconverted to a sulfate by fuming with sulfuric acid. On analysis thesample thus obtained was observed to contain element 95 in the amount of1.4 10 c./m. The precipitate which had been fumed with sulfuric acid wasdissolved in water, precipitated as the hydroxide and then dissolved innitric acid, and the resulting solution evaporated completely to drynessto remove excess acid. This residue was then dissolved in 2 1. of 0.1 Mnitric acid, after which was added thereto a 30% solution of hydrogenperoxide which resulted in the precipitation of the plutonium presenttherein. Radioassay of the precipitate indicated that 5 g. of plutoniumhad been removed. This procedure was repeated, precipitating from aneven smaller volume (0.75 l.) with very little, if any, plutoniumperoxide being formed. The amount of plutonium remaining with element 95appeared to be very insignificant. A count of the entire sample was madein a vacuum low geometry chamber. The total count of element 95 wasfound to be1.13 10 c./m.

It is to be understood that the specific compounds described above andthe foregoing examples are merely illustrative of the present inventionand are in no way to be construed as limitative thereof. It will beapparent to those skilled in the art that the general procedure set outin the above description is susceptible of numerous modificationswithout departing from the spirit of the present invention. For example,it should be noted that while element 95 can be removed from solutionsof neutron irradiated uranium or plutonium by means of the carriermethods herein set forth, said element may also be removed from otheraqueous or non-aqueous liquid media in addition to those resulting fromthe solution of uranium or plutonium in a suitable acid utilizingmethods similar in principle to those herein set forth.

What is claimed is:

1. In a process for the synthesis of element 95, the steps whichcomprise dissolving a neutron-irradiated mass of uranium containing atransuranic fraction comprising predominantly plutonium which containsat least about 0.01% of the isotope 94 and a detectable quantity ofelement 95 in an aqueous acidic solution, oxidizing the plutoniumcontained in the resulting solution to a valent state greater than +4,removing uranium fission products and element 95 therefrom by means of awater-insoluble rare earth salt carrier, dissolving the carrierprecipitate thus obtained, introducing fluosilicate ions into theresulting solution, contacting said solution with a water-insoluble rareearth salt carrier for said fission products and separating theresulting precipitate, adding suflicient hydrofluoric acid to render thesupernatant solution thus obtained from about 3 to 6 M with respectthereto, thereafter contacting the solution with a waterinsoluble rareearth salt carrier for element 95, and separating the carrierprecipitate from the solution.

2. In a process for the synthesis of element 95, the steps whichcomprise dissolving a neutron-irradiated mass of uranium containing atransuranic fraction comprising predominantly plutonium which containsat least about 0.01% of the isotope 94 and a detectable quantity ofelement 95 in an aqueous acidic solution, oxidizing the plutoniumcontained in the resulting solution to a valent state greater than +4,removing element 95 and uranium fission products which include bariumand zirconium and rare earth metals by means of a Waterinsoluble rareearth salt carrier, dissolving the carrier precipitate thus obtained,separating the barium contained in the supernatant solution from element95 and the other uranium fission products by precipitating said productsand element 95 in the form of their hydroxides leaving barium insolution, separating the resultant precipitate and dissolving saidprecipitate in an aqueous acidic solution, contacting the resultantsolution with a water-insoluble rare earth salt zirconium carrier,separating the supernatant solution from the carrier precipitate,dissolving this precipitate in an aqueous acidic solution, introducingfluosilicate ions into the resulting solution, contacting said solutionwith a water-soluble rare earth salt carrier for said fission productsand separating the resulting precipitate, adding suflicient hydrofluoricacid to render the solution from about 3 to 6 M with respect thereto,thereafter contacting the solution with a water-insoluble rare earthsalt carrier for element 95, and separating the carrier precipitate fromthe solution.

3. The process of claim 2 in which lanthanum fluoride is used as thecarrier for element 95.

4. The process of claim 2 in which cerous fluoride is used as thecarrier for element 95.

5. The process of claim 2 in which ceric iodate is used as the carrierfor zirconium and a rare earth fluoride is used as the carrier forelement 95.

6. In a process for the removal of element 95 from a solution containingsaid element and rare earth fission products, the steps which compriseintroducing fluosilicate ions into the solution, contacting saidsolution with a water-insoluble rare earth salt carrier for said rareearth fission products and separating from the solution the precipitatethus formed, adding sufficient hydrofluoric acid to render the solutionfrom about 3 to 6 M with respect thereto, thereafter contacting thesolution with a waterinsoluble rare earth salt carrier for element 95,and separating the carrier precipitate from the solution.

7. The process of claim 6 in which the carrier employed in both steps iscerous fluoride.

8. The process of claim 6 in which the carrier employed in both steps islanthanum fluoride.

9. In a process for the removal of element from a solution containingsaid element and rare earth fission products, the steps which compriseintroducing fluosilicate ions into the solution, contacting saidsolution with a water-insoluble rare earth salt carrier for said rareearth fission products and separating from the solution the precipitatethus formed, thereafter contacting the solution with a water-insolublerare earth salt carrier for element 95 in the presence or 3-6 Mhydrofluoric acid, and separating the carrier precipitate from thesolution.

10. A method of separating element 95 from rare earth elements whichcomprises precipitating an insoluble rare earth compound from an aqueoussolution containing element 95, a rare earth element, and afluosilicate.

11. In a process for the synthesis of element 95, the steps whichcomprise subjecting natural uranium to a self-sustaining neutronic chainreaction for a period of time sufiicient to produce a transuranicfraction comprising predominantly plutonium which contains at leastabout 0.01% of the isotope 94 aging said plutonium for a further periodof time such that said isotope present therein decays into a detectablequantity of element 95, dissolving the aged product in an aqueous acidicsolution, oxidizing the plutonium contained in the resulting solution toa valent state greater than +4, removing element 95 and uranium fissonproducts which include barium and zirconium and rare earth metals bymeans of a waterinsoluble rare earth salt carrier, dissolving thecarrier precipitate thus obtained, separating the barium contained inthe supernatant solution from element 95 and the other uranium fissionproducts by precipitating said products and element 95 in the form oftheir hydroxides leaving barium in solution, separating the resultantprecipitate and dissolving said precipitate in an aqueous acidicsolution, contacting the solution with a water-insoluble rare earth saltzirconium carrier, separating the supernatant solution from the carrierprecipitate, dissolving this precipitate in an aqueous acidic solution,introducing fluosilicate ions into the resulting solution, contactingsaid solution with a water-insoluble rare earth salt carrier for saidfission products and separating the resulting precipitate, thereaftercontacting the solution in the presence of 3-6 M hydrofluoric acid witha water-insoluble rare earth salt carrier for element 95, and separatingthe carrier precipitate from the solution.

References Cited Chem. Eng. News 23 (1945), 21903; 24, 1193-8 (1946);24, 3160-1 (1946); 25, 1509 (1947).

Chem. Education, 22, 61923 (1945).

CARL D. QUARFORTH, Primary Examiner H. E. BEHREND, Assistant ExaminerU.S. Cl. X.R.

1. IN A PROCESS FOR THE SYNTHESIS OF ELEMENT 95, THE STEPS WHICHCOMPRISE DISSOLVING A NEUTRON-IRRADIATED MASS OF URANIUM CONTAINING ATRANSURANIC FRACTION COMPRISING PREDOMINANTLY PLUTONIUM WHICH CONTAINSAT LEAST ABOUT 0.01% OF THE ISOTOPE 94**241 AND A DETECTABLE QUANTITY OFELEMENT 95 IN AN AQUEOUS ACIDIC SOLUTION, OXIDIZING THE PLUTONIUMCONTAINED IN THE RESULTING SOLUTION TO A VALENT STATE GREATER THAN +4,REMOVING URANIUM FISSION PRODUCTS AND ELEMENT 95 THEREFROM BY MEANS OF AWATER-INSOLUBLE RARE EARTH SALT CARRIER, DISSOLVING THE CARRIERPRECIPITATE THUS OBTAINED, INTRODUCING FLOUSILICATE IONS INTO THERESULTING SOLUTION, CONTACTING SAID SOLUTION WITH A WATER-INSOLUBLE RAREEARTH SALT CARRIER FOR SAID FISSION PRODUCTS AND SEPARATING THERESULTING PRECIPITATE, ADDING SUFFICIENT HYDROFLUORIC ACID TO RENDER THESUPERNATANT SOLUTION THUS OBTAINED FROM ABOUT 3 TO 6 M WITH RESPECTTHERETO, THEREAFTER CONTACTING THE SOLUTION WITH A WATER-INSOLUBLE RAREEARTH SALT CARRIER FOR ELEMENT 95, AND SEPARATING THE CARRIERPRECIPITATE FROM THE SOLUTION.